Euler's phi function defined $(n)$ as the number of positive integers smaller than a given number $n$ that are relatively prime to $n.$ For example, $(10)=4($the numbers $1,3,7$ and $9).$ The value of $(7)+(9)+(12)-(15)$ is

a$)6$

b$)7$

c$)8$

d$)9$

e$)10$